The metal-oxide-semiconductor field-effect transistor (MOSFET) is a common transistor used in the production of integrated circuits. During the fabrication of a MOSFET, silicide layers may be used to improve the conductivity of polysilicon-containing active regions of the MOSFET. For instance, silicide may be formed on the source and drain regions of a MOSFET to improve their conductivity. The silicide layer has better electrical properties than the polysilicon alone.
The process in which silicide is formed is often called salicide (i.e., self-aligned silicide). The process to form salicide begins by depositing a thin transition metal layer, such as a nickel layer, onto the polysilicon-containing active regions of the device. The metal and a portion of the polysilicon are then alloyed together to form the silicide layer. For instance, if nickel is used, the nickel reacts with the polysilicon to form nickel silicide. The alloying process may include a series of annealing and/or etch processes. Following the silicide formation, any remaining transition metal may be removed by chemical etching, leaving silicide layers in only the active regions of the MOSFET.
An atomic layer deposition process may be used to form the thin nickel metal layer. Unfortunately, in conventional processes, the metal layers that are formed have an unacceptably high amount of carbon incorporation. The carbon content is generally greater than 5%. The presence of carbon may increase the resistivity of the silicide layer. Accordingly, there is a need for salicide processes that generate nickel silicide layers with low carbon content.